Head Mounted Display with Eye Tracking

1. A head-mounted optical device, comprising: one or more projection light sources; one or more eye-tracking light sources; a polarizing beam splitter; and a second polarizing beam splitter; wherein the optical device is configured such that projection light from the one or more projection light sources and eye-tracking light from the one or more eye-tracking light sources are both at least partially reflected by the polarizing beam splitter; and wherein the optical device is configured such that an optical path between the polarizing beam splitter and the second polarizing beam splitter for at least one of projection light from the one or more projection light sources and eye-tracking light from the one or more eye-tracking light sources passes through air, wherein the polarizing beam splitter and the second polarizing beam splitter have different right band edges, and substantially equal left band edges.

2. The head-mounted optical device of claim 1 , wherein the eye-tracking light from the one or more eye-tracking light sources includes infrared light.

3. The head-mounted optical device of claim 1 , wherein a eye-tracking wavelength range of the eye-tracking light from the one or more eye-racking light sources and a projection wavelength range of the projection light from the one or more projection light sources do not overlap.

4. The head-mounted optical device of claim 1 , wherein the polarizing beam splitter reflects at least 50% of both a first polarization state and a second orthogonal polarization state of eye-tracking light from the one or more eye-tracking light sources.

5. The head-mounted optical device of claim 4 , wherein the polarizing beam splitter reflects at least 50% of a first polarization state but less than 50% of a second orthogonal polarization state of projection light from the one or more projection light sources.

6. The head-mounted optical device of claim 1 , wherein the polarizing beam splitter is immersed in a lens.

7. The head-mounted optical device of claim 1 , wherein at least one of the polarizing beam splitter and the second polarizing beam splitter include multilayer optical film.

8. The head-mounted optical device of claim 1 , wherein the eye-tracking light from the one or more eye-tracking light sources includes a substantial portion of light with a wavelength between 700 and 1000 nm.

9. The head-mounted optical device of claim 1 , wherein the polarizing beam splitter reflects at least 50% of a first polarization state but less than 50% of a second orthogonal polarization state of eye-tracking light from the one or more eye-tracking light sources.

10. The head-mounted optical device of claim 1 , wherein the second polarizing beam splitter transmits at least 50% of both a first polarization state and a second orthogonal polarization state of eye-tracking light from the one or more eye-tracking light sources.

11. The head-mounted optical device of claim 1 , further comprising a quarter wave plate.

12. The head-mounted optical device of claim 1 , further comprising an image sensor.

13. The head-mounted optical device of claim 12 , wherein the image sensor includes a CCD imager.

14. The head-mounted optical device of claim 12 , wherein the image sensor includes a CMOS imager.

15. The head-mounted optical device of claim 12 , further comprising a frame, wherein the image sensor is disposed within the frame.

16. A head-mounted optical device, comprising: one or more projection light sources; one or more eye-tracking light sources; a polarizing beam splitter; and a second polarizing beam splitter; wherein the optical device is configured such that projection light from the one or more projection light sources and eye-tracking light from the one or more eye-tracking light sources are both at least partially reflected by the polarizing beam splitter; and wherein as measured between 40 degrees and 50 degrees in a medium with a refractive index of about 1.53, the polarizing beam splitter has a right band edge between about 950 nm and about 850 nm.

17. The head-mounted optical device of claim 16 , wherein as measured between 40 degrees and 50 degrees in a medium with a refractive index of about 1.53, the second polarizing beam splitter has a right band edge between about 800 nm and about 700 nm.